Still



Patented June 29, 1954 STILL Robert J. Schmidt, Oakland, and Sam Rosenfeld, Berkeley, Calif, assignors to the United States of America as represented by the United States Atomic Energy Commission Application October 7, 1943, Serial No. 505,324

9 Claims.

1. The present invention relates to distillation apparatus. The invention relates still more particularly to distillation apparatus comprising a molecular still that is particularly useful in eonjunction with the production and purification of chlorides of uranium.

It is an object of the present invention to provide an improved distillation apparatus.

Another object of the invention is to provide an improved apparatus adapted for the vaporization and/or sublimation of materials having volatilization characteristics similar to those of UCL; and UCls.

A further object of the invention is to provide an improved molecular still that is particularly adapted for use in the improved processes of producing and purifying U014 and U016.

A further object of the invention is to provide a still of improved construction and arrangement that is efficient in operation.

The invention, both as to its organization and method of operation together with. further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing in which the single figure is a perspective view, partly broken away, of a molecular still embodying the present invention.

Referring now more particularly to the single figure of the drawing, there is illustrated a molecular still It that embodies the features of the present invention and comprises upper and lower casing sections I I and I2, respectively. The upper casing section II is of substantially cup-shaped configuration including a cylindrical side wall it and a fiat top wall i l; while the lower casing section I2 is of substantially cup-shaped configuration including a cylindrical side wall I5 and a flat bottom wall I6. The open lower end of the upper casing section II is secured to an annular sealing flange IT and the open upper end of the lower casing section I2 is secured to an annular sealing flange I8; the sealing flanges I! and It being provided with polished abutting surfaces and removably secured together by a series of bolts I9 extending through aligned openings formed therein.

Two concentrically arranged grooves are formed in the lower surface of the sealing flange I! and receive two ring-shaped gaskets 2i} and it which are retained under compression, thereby to provide a gas-tight seal between the sealing flanges H and I8, whereby the upper and lower casing sections II and I2 form an hermetically sealed enclosure. Also, an annular re- 2 cess 22 is formed in the lower surface of the sealing flange ll and positioned between the two concentric grooves in which the two ring-shaped gaskets 20 and 2i are disposed. A restricted opening 23 is formed in the sealing flange I! and communicates both with the annular recess 22 and a conduit 24, the inner end of which is secured to the upper surface of the sealing flange IT. The outer end of the conduit 24 is connected to a pressure gauge and vacuum pumping apparatus, not shown. This arrangement provides for ready testing of the efiiciency of the gaskets 20 and 2 I; which test may be performed merely by initiating operation of the vacuum pumping apparatus, whereby the conduit 24 and the recess 22 are exhausted, the pressure being indicated by the pressure gauge. In View of the fact that the conduit 24 is sealed directly to the sealing flange ii and communicates only with the opening 23, which in turn communicates only with the recess 22, the pressure gauge should indicate an immediate-and rapid reduction of pressure in the conduit 24 unless one of the gaskets 20 or H is leaking.

Also, the molecular still It comprises an inverted substantially cup-shaped heater 25 which is adapted to be brought into good heat exchange relation with respect to the top wall I l and the upper portion of the cylindrical side wall I3. Preferably, the heater 25 comprises a composite structure and is of the adjustable electric type, whereby the temperature thereof and consequently the temperature of the upper casing section II may be selectively controlled, Further, the heater 25 is suitably mounted upon a support, not shown, whereby it may be raised and lowered with respect to the upper casing section I I in an obvious manner.

Further, the molecular still It comprises an arrangement for cooling the extreme lower portion of the cylindrical side wall II, the sealing flanges I! and I8, the cylindrical side wall I5, and the bottom wall I6; which arrangement comprises two cooling coils 26 and 27 adapted union Preferably, the cooling coil 25 is to be detachably joined together by a suitable formed of copper and is securely attached to the lower casing section H2 in good heat exchange relation therewith, while the cooling coil 21 is formed of copper and is securely attached to the upper casing, section II in good heat exchange relation therewith. More particularly, the cooling coil 28 is soldered or otherwise ailixed to the bottom wall It, the cylindrical side wall I5 and the sealing flange I8; the cooling coil 26 Winding first around the bottom wall I6, then around the lower portion of the cylindrical side wall I5, then around the upper portion of the cylindrical side wall I5 just below the sealing flange I8, then around the peripheral edge of the sealing flange I3, and terminating at the union 28. Similarly, the cooling coil 21 is soldered or otherwise aflixed to an annular flange 29 disposed about the extreme lower end of the upper casing section II and the sealing flange IT; the cooling coil 21 winding first around the annular flange 29, then around the peripheral edge of the sealing flange I1, and terminating at the union 23. The annular flange 29 is formed about the extreme lower end of the upper casing section II by an annular groove 39 cut in the outer surface of the cylindrical side wall I3. The annular groove is disposed between the annular flange 29 and the lower portion of the cylindrical side wall I3, thereby to provide a relatively thin connecting wall 3| extending therebetween; whereby the transfer of heat from the cylindrical side wall I3 disposed within the heater 25 to the annular flange 29 is minimized. The outer end of the cooling coil 26 is connected to a suitable water supply source, not shown, while the outer end of the cooling coil 21 is connected to a suitable drain, not shown; whereby the bottom wall I6, the cylindrical side wall I5, the sealing flanges i8 and IT, and the annular flange 29 are cooled. Thus, in general, the upper casing section II is heated and the lower casing section I2 is cooled.

The hermetically sealed enclosure formed by the upper and lower casing sections II and I2 houses removable upper and lower containers 32 and 33, respectively. The lower container 33 is of substantially cup-shaped configuration, including a cylindrical side wall 34 and a flat bottom wall 35; while the upper container 32 is of substantially cup-shaped configuration, including a cylindrical side wall 33 and a flat bottom wall 37. The lower container 33 is arranged in the lower portion of the hermetically sealed enclosure, the bottom wall 35 resting directly upon the bottom wall I6, and the cylindrical side wall 34 closely fitting the cylindrical side wall 15 and the lower portion of the cylindrical side wall I3. The upper container 32 is arranged in the upper portion of the hermetically sealed enclosure, and is supported by the lower container 33, the lower rim of the cylindrical side wall 36 resting directly upon the upper rim of the cylindrical side wall 34, the cylindrical side wall 36 closely fitting the intermediate portion of the cylindrical side wall I3, and the upper rim of the cylindrical side wall 36 terminating below the top wall I4. Accordingly, the upper container 32 is supported by the lower container 33 and is arranged in good heat exchange relation with the upper casing section I I, while the lower container 33 is supported by the lower casing section I2 and is arranged in good heat exchange relation with the lower casing section I2, the sealing flanges I1 and I8 and the annular flange 29. Thus the upper container 32 may be heated by the heater 25 and the lower container 33 may be cooled by the cooling arrangement including the cooling coils 26 and 21.

The upper container 32 houses partition structure 38 arranged within the cylindrical side wall 36 and defining a number of compartments adapted to receive a charge to be vaporized. More particularly, the partition structure 38 comprises upstanding walls 39 and 40 arranged substantially mutually normal to each other and to the bottom wall 3'1, and having a substantially T-shaped cross section defining three compartments within the upper container 32. Preferably, the upstanding walls 39 and 40 extend from the bottom wall 31 to the upper rim of the side wall 36 and are secured both together and to the walls 36 and 31 by welded joints; whereby the partition structure 38 is arranged in good heat exchange relation with the walls 36 and 3'! of the upper container 32 in order to insure substantially uniform heating of the charge in the three compartments mentioned. Preferably, the upstanding wall 39 is disposed to one side of the longitudinal plane bisecting the upper container 32, whereby the three compartments mentioned have substantially identical volumes, two of the compartments being of identical configuration and the third compartment being of a diiferent configuration, as will be apparent from inspection.

Also, a longitudinally extending depression 4| is formed in the cylindrical side wall 36 of the upper container 32 in substantial alignment with the upstanding wall 40, whereby the third compartment mentioned has a substantially bowshaped configuration. Thus the depression 4I formed in the cylindrical side wall 36 of the upper container 32 provides a wall arranged in spaced-apart relation with the adjacent cylindrical side wall I3 of the upper casing section II, defining a passage 42 communicating between the upper and lower containers 32 and 33. The upper end of the passage 42 communicates with the space disposed above the three compartments mentioned formed in the upper container 32, which space lies between the lower surface of the top wall I4 and the upper edge of the walls 36, 39 and 40. On the other hand, the lower end of the passage 42 communicates directly with the upper end of the lower container 33 inwardly from the cylindrical side wall 34 thereof.

The lower container 33 is adapted to receive and condense the vapor from the passage 42 communicating between the upper and lower containers 32 and 33, and houses removable baffle structure 43 disposed in the lower portion thereof and covering an opening 44 formed in the cylindrical side wall 34. More particularly, one end of an evacuation conduit 45 is secured in an opening formed in the cylindrical side wall I5 of the lower casing section I2; which conduit communicates via the opening 44 directly with the interior of the lower container 33 and consequently via the passage 42 to the interior of the three compartments defined in the upper container 32, the opening 44 registering with the evacuation conduit 45. The outer end of the conduit 45 is connected to suitable vacuum pumping apparatus, not shown; whereby the hermetically sealed enclosure defined by the upper and lower casing sections II and I2 may be suitably evacuated. 'More particularly, the baffle structure 43 comprises two upstanding bowed strips 46 and 41 and a horizontal segmental plate 48 secured together in mutually spaced-apart relation to form a removable composite structure. The bowed strip 46 is supported by the bottom wall 35 and extends between two spaced-apart portions of the cylindrical side wall 34; the segmental plate 48 fits the cylindrical side wall 34 between the two spacedapart portions mentioned, and overhangs the bowed strip 46; and the bowed strip 41 extends between the two spaced-apart portions mentioned of the cylindrical side wall 34 and extends both above and below the slot formed between the bowed strip 46 and the segmental plate 48. Accordingly, the baffle structure 43 defines upper and lower sinuous baiiled passages between the interior-of the lower container 33 and the opening 44 formed in the cylindrical side wall 34, and registering with the evacuation conduit 45; whereby surfaces are provided which tend to condense vapor as sublimate in the interior of the lower container 33, thus preventing the flow of sublimate into the evacuation conduit 45.

When designed for subliming uranium chlorides (for which purpose the still of the present invention is particularly well adapted, and in connection with which the operation thereof is described in detail herein for illustrative pur-- poses), the various parts of the upper and lower containers 32 and 33, as well as the baiilestructure 43, are formed of a metal which is not readily attacked by the hot uranium chlorides, U014, UC and UCls. Also, at least the cylindrical side wall [3 and the top wall M of the upper casing section II are formed of the metal mentioned; and it is well to form the cylindrical side wall i5 and the bottom wall it of the lower casing section l2 of this metal. Also, the metal from which the parts mentioned are fabricated should not cause undue catalytic decomposition of the higher uranium chlorides, particularly UCle. For example, the parts mentioned of the molecular still [6 may be formed of stainless steel, as such metal is not readily attacked by the hot uranium chlorides and it does not cause undue catalytic decomposition of the higher uranium chlorides.

In the operation of the molecular still ill, the lower container 33 is placed in the lower casing section 12 in such position that the opening 44 formed in the cylindrical side wall 34 registers with the evacuation conduit 45; and the baffle structure 43 is placed within the lower container 33 in proper baffling relation with respect to the opening 44 formed in the cylindrical side wall 34 and the associated evacuation conduit 45. A suitable charge to be vaporized or sublimed is loaded in the three compartments mentioned formed in the upper container 32, and the upper container 32 is placed upon the lower container 33 in alignment therewith and in such position that the depression 4i formed in the cylindrical side wall 3E5 is disposed substantially diametrically opposite to the opening 44 formed in the cylindrical sid wall 34 and the associated evacuation conduit 45. The upper casing section I l is then brought into place and slid over the aligned containers 3 2 and 33 such that the sealing flanges H and i8 are engaged and the ends of the cooling coils 26. and 21 are disposed in proper relation with respect to the union 28. The bolts I9 are then placed in the openings formed in the sealing flange l1 and threaded into firm engagement in the cooperating threaded openings formed in the sealing flange l8, whereby the sealing flanges H and 18 are securely fastened together. The union 28 is manipulated to join the adjacent ends of the cooling coils 2e and 21.

At, this time the seal between the sealing flanges I1 and I8 may be appropriately tested by initiating operation of the vacuum pumping apparatus connected to the conduit 24, whereby the recess 22 is exhausted, the pressure therein being indicated by the associated pressure gauge. In theevent either of the gaskets 23' or 2! leaks, the pressure gauge associated with the conduit 24 will fail toindicate an immediate and rapid reduction of pressure in the conduit 24 and the connected recessfiywhereby the bolts I 9 may be further tightened in order to perfect the seal between the sealing flanges l1 and I8. Assuming that the seal between the sealing flanges I! and I8 is in proper condition, the operation of the vacuum pumping apparatus associated with the conduit 24 may be arrested as it serves no further utility. At this time, the upper and lower casing sections H and [2 have been secured together to form an hermetically sealed enclosure housing the upper and lower containers 32 and 33 in the manner previously noted.

Operation of the vacuum pumping apparatus associated with the evacuation conduit 45 is then initiated, whereby a suitable vacuum is drawn in the hermetically sealed enclosure formed by the upper and lower casing sections i I and I2. At this time the heater 25 is lowered and brought into relation with the upper casing section II and cooling water is conducted through the connected cooling coils 26 and 27. Accordingly, the

heater 25 heats the cylindrical side wall #3 and the top wall M of the upper casing section H, whereby the cylindrical side wall 36 of the upper container 32 is heated and heat is conductedthrough the connected walls 39 and 45 of the partition structure 38, in order to cause substantantially uniform heating of the charge in the three compartments defined in the upper container 32. On the other hand, the cooling arrangement, including the cooling coils 26 and 21, cools the cylindrical side wall l5 and the bottom wall It of the lower casing section 12, the sealing flanges ll and Iii and the annular flange 29, whereby the cylindrical side wall 34 and bottom wall 35 of the lower container 33 are cooled. Also, the baffle structure 43, being disposed in good heat exchange relation with respect to the cylindrical side wall 34 and the bottom wall 35 of the lower casing section 33, is appropriately cooled. Further, the thin connecting wall 3i disposed between the cylindrical side wall 13 and the annular flange .29 restricts the amounts of heat conducted therebetween and consequently minimizes the flow of heat. directly from the heater 25 into the cooling arrangement including the cooling coils 26 and 2?, in an obvious manner.

When the charge contained in the three cornpartments formed in the upper container 32 is thus heated, it is vaporized or' sublimed, filling the space disposed just below the top wall I4 of the upper casing section II and communicating with the passage 42. Thus the vapor isconducted through the passage 42 into the interior of the lower container 33; the walls defining the passage 42 being hot prevents the condensation of the vapor in the passage 42- and insuresi'ts d'e-- livery into the interior of the lower container 3 3.- The vapor contacting the cool walls of the lower container 33 is condensed thereon, some of the vapor being condensed on the cool balile structure 43. It will be understood that the baiile structure 43 prevents unrestricted flow of the vapor in the lower container 33' through the opening 44 formed in the cylindrical side wall 34 into the evacuation conduit 45, whereby substantially none of the vapor is lost incident to operation of" the molecular still H].

In the molecular still 53, the transfer of the vapor from the upper container 32 to the lower container 33 is due to the thermal energy of the vaporized molecules. The vacuum drawn in the hermetically sealed enclosure mentioned is high, and consequently the pressure therein is so low that the mean free path of the molecules" is 01 the order of the dimensions of the evacuated space. Such a pressure is achieved within the pressure range 10- to 10- mm. Hg. Thus the molecules, after escaping from the hot surface of the upper container 32 and after a very few collisions with the heated walls of the upper enclosure provided by the upper casing section 11 and the passage 42, collide with the cold walls of the lower container 33 or the baffle structure 43, and are condensed thereon.

Thus it will be understood that the molecular still is very useful in the vaporization or sublimation of charges which may be readily purifled utilizing a process of this general character.

By way of description of an illustrative use of the still constituting the present invention, there is described a process for producing and separating U014 and U016 which may be carried out therein in the following manner. More particularly, an appropriate charge of U015 is placed in the three compartments mentioned, formed in the upper container 32, the charge being tamped in place so that it completely fills the three compartments. The parts of the molecular still 10 are assembled in the manner previously explained; the hermetically sealed space defined by the upper and lower casing sections 11 and I2 is evacuated, whereby a pressure between 10" and 10 mm. Hg is established therein; the cooling arrangement is adjusted; and the heater 25 is brought into relation and adjusted. More particularly, the cooling arrangement is adjusted whereby the temperature of the bottom wall 16 of the lower casing section 12 is maintained at a temperature of the order of 40 0., and the temperature of the lower container 33 is maintained at only a slightly higher temperature due to the necessary temperature gradient therebetween; and the heater 25 is adjusted, whereby the temperature of the cylindrical side wall 13 of the upper casing section II is maintained at a temperature between 200 and 220 0., and the temperature of the upper container 32 is maintained at a somewhat lower temperature due to the necessary temperature gradient therebetween, causing the temperature of the charge in the three compartments in the upper container 32 to be maintained at a still slightly lower temperature due to the necessary temperature gradient between the charge and the upper container 32. More specifically, the charge is maintained at a temperature of the order of 180 0.

When the charge of U015 is thus subjected to the heating and reduced pressure treatment mentioned, it is decomposed into U014 and U016, as disclosed in the copending application of Francis A. Jenkins, Serial No. 494,447, filed July 13, 1943, which was issued as U. S. Patent No. 2,572,156 on October 23, 1951. As the U015 is thus decomposed, the U014 produced remains in the upper container 32 as a residue, in view of the fact that the vapor pressure thereof is practically zero at the temperature mentioned; while the UCIG produced is sublimed, in view of the fact that the vapor pressure thereof is relatively substantial, e. g. of the order of 18 mm. of mercury at the temperature mentioned. The vapor of U016 is conducted through the passage 42 communicating between the upper container 32 and the lower container 33, and is condensed in the lower container 33.

The process is continued until the charge of U015 is substantially completely converted, at which time the residue remaining in the upper container 32 is substantially chemically pure U014 and the sublimate collected in the lower container 33 is substantially chemically pure U016. At this time, when further production and sublimation of U016 ceases, the process is complete; the heater 25 is removed from the upper casing section II; operation of the vacuum pumping apparatus associated with the evacuation conduit 45 is arrested; and the operation of the cooling arrangement is continued until the molecular still II] has cooled to the ambient temperature. The operation of the cooling arrangement is then arrested and the molecular still 10 is disconnected from the associated parts and transferred to a dry cabinet containing 002 or a suitable inert gas. The molecular still I0 is then opened in the cabinet, and the U014 in the upper container 32 and the UC16 in the lower container 33 are separately collected and bottled by any suitable remotely controlled means, such as used in the handling of toxic or hygroscopic materials. Since such means are conventional and form no novel portion of our invention, no description thereof is incorporated herein. The two products, U014 and U016, are separately bottled in an atmosphere of 002 orin a vacuum, and sealed for future use. The precautions mentioned must be taken in view of the fact both the products U014 and UClG, are very hygroscopic and decompose in the presence of ordinary air containing moisture.

It has been found that the vapor pressuretemperature curves of U016 and U014. are of usual configuration showing the vapor pressure increases disproportionately With temperature, i. e. exhibits a sharp rise in a short range of temperatures. Also, the curves are substantially spaced on the temperature scale. .Thus the vapor pressure of U014 is negligible up to temperatures well above those at which U016 exhibits a substantial vapor pressure, so that especially under the vacuum conditions of the present procedure, U016 may be separated from U014 by sublimation at temperatures providing satisfactory yields of U016, and with little or no appreciable sublimation of U014. The foregoing will be ap-- parent from the following table of vapor pressures:

wen

l Decomposition of UCh begins. 2 Vapor pressure of U014 below 300 C. is negligible.

In employing the molecular still 10 in the manner described above, wherein the upper container 32 is adapted to accommodate a charge of 2200 grams of U015, a time interval of approximately fourteen hours is normally required in order to obtain substantially complete conversion of the charge of U015 into U014 and UC16. The decomposition of the U015 is substantially quantitative, and in this example the yield should be approximately 1007 grams of U014 andll93 grams of U016; yields very closely approximating that indicated may be readily obtained.

The residue remaining in the upper container 32 was collected and bottled as U014, and the sublimate in the lower container 33 was collected and bottled as U016. As a matter of fact, as the process is practiced, the sublimate collected from the lower container 33 frequently contains U014 as an impurity resulting from some decomposition of the U016; while the residue collected from the upper container 32 frequently contains other impurities, in that the original charge of U015 frequently contains small amounts of uranium oxides and oxychlorides which are not vaporized or sublimed. The U016 may be further purified in order to eliminate therefrom the contained U014, and the U014 may be further purified in order to eliminate therefrom the contained uranium oxides, such as U02, U03, and U308, and the uranium oxychlorides, such as UO2C12, (30014, and possibly UOClz.

By way of description of a further illustrative use of the still constituting the present invention, there is described a process for purifying U014 which may be carried out therein in the following manner. More particularly, an appropriate charge of U014 is placed in the three compartments mentioned formed in the upper container 32, the charge being tamped in place so that it completely fills the three compartments.

The parts of the molecular still ii) are assembled in the manner previously explained; the hermetically sealed space defined by the upper and lower casing sections II and ii. is evacuated, whereby a pressure between and 10 mm. Hg is established therein, the cooling arrangement is adjusted; and the heater 25 is brought into relation and adjusted. More particularly, the cooling arrangement is adjusted, whereby the temperature of the bottom wall 16 of the lower casing section 12 is maintained at a temperature of the order of 40 0., and the temperature of the lower container 33 is maintained at only a slightly higher temperature due to the necessary temperature gradient therebetween; and the heater 25 is adjusted, whereby the temperature of the cylindrical side wall 13 of the upper casing section II is maintained at a temperature between 650 and 675 0., and the temperature of the upper container 32 is maintained at a somewhat lower temperature due to the necessary temperature gradient therebetween, causing the temperature of the charge in the three compartments in the upper container 32 to be maintained at a still slightly lower temperature due to the necessary temperature gradient between the charge and the upper container 32. More specifically, the charge is maintained at a temperature of the order of 600 0.

When the charge is thus subjected to the heating and reduced pressure treatment mentioned, the U014 therein is sublimed in view of the fact that the vapor pressure thereof is relatively substantial at the temperature mentioned; while the uranium oxides and uranium oxychlorides remain in the upper container 32 as a residue in View of the fact that the vapor pressures thereof are practically zero or negligible at or even considerably above the temperature mentioned. The vapor of U014 is conducted through the passage 42 communicating between the upper Ill.

10 container 32 and the lower container 33, and is condensed in the lower container 33.

The process is continued until substantially all of the U014 in the charge is sublimed, at which time the residue remaining in the upper con tainer 32 comprises a mixture of the various uranium oxides and oxychlorides and the sublimate collected in the lower container 33 is substantially chemically pure U014. At this time, when further sublimation of U014 in the charge ceases, the process is complete; the heater is removed from the upper casing section H; operation of the vacuum pumping apparatus associated with the evacuation conduit 35 is arrested; and the operation of the cooling arrangementis continued until the molecular still it has been cooled to the ambient temperature. The operation of the cooling arrangement is then arrested and the molecular still in is disconnected from the associated parts and transferred to a dry cabinet containing 002 or a suitable inert gas. The molecular still H] is then opened and the U014 in the lower container 33 is collected and bottled in an atmosphere of 002 or in a vacuum and sealed for future use. In so handling the hygroscopic materials, any suitable remotely controlled means, the exact nature of which forms no novel portion of our invention, may be used. The residue remaining in the upper container 32 may be separately collected and subsequently re-worked in order to produce any standard uranium compound, such, for example, as U015, in any suitable manner. The precautions mentioned must be taken in view of the fact that the U014 is very hygroscopic and decomposes in the presence of ordinary air containing moisture.

In employing the molecular still it] in the manner described above, wherein the upper container 32 is adapted to accommodate a charge of 2400 grams of U014, a time interval of approximately three hours is normally required in order to obtain substantially complete sublimation of the chemically pure U014 in the charge. Charges containing as much as two per cent impurities may be readily purified in order to produce sub" stantially chemically pure U014, the product analyzing as high as 99.9% U014.

By way of description of yet another illustrative use of the still constituting the present invention, there is described a process for purifying U016 which may be carried out therein in the following manner. More particularly, an appropriate charge of UCIS is placed in the three compartments mentioned formed in the upper container 32, the charge being tamped in place so that it completely fills the three compartments. The parts of the molecular still it! are assembled in the manner previously explained; the hermetically sealed space defined by the upper and lower casing sections H and i2 is evacuated, whereby a pressure between l0 and 10* mm. Hg is established therein; the cooling arrangement is adjusted; and the heater Z5 is brought into relation and adjusted. More particularly, the cooling arrangement is adjusted, whereby the temperature of the bottom'wall iii of the lower casing section 12 is maintained at a temperature of the order of 40 0., and the temperature of the lower container is maintained at only a slightly higher temperature due to the necessary temperature gradient therebetween; and the heater 25 is adjusted, whereby the temperature of the cylindrical side wall 53 of the upper casing section II is maintained at a temperature between 200 and 220 C., and the temperature of the upper container 32 is maintained at a somewhat lower temperature due to the necessary temperature gradient therebetween, causing the temperature of the charge in the three compartments in the upper container 32 to be maintained at a still slightly lower temperature due to the necessary temperature gradient between the charge and the upper container 32. More specifically, the charge is maintained at a temperature of the order of 180 C.

When the charge is thus subjected to the heating and reduced pressure treatment mentioned, the 11016 therein is sublimed in view of the fact that the vapor pressure thereof is relatively substantial at the temperature mentioned, while any U014 mixed in the charge remains in the upper container 32 as a residue in view of the fact that the vapor pressure thereof is practically zero, at and even considerably above the temperature mentioned. The vapor of UCls is conducted through the passage 42* communicating between the upper container 32 and the lower container 33, and is condensed in the lower container 33.

The process is continued until substantially all of the UClG in the charge is sublimed, at which time the residue remaining in the upper container 32 comprises essentially UCL; and the sublimate collected in the lower container 33 is substantially chemically pure U C16. At this time, when further sublimation of U016 in the charge ceases, the process is complete; the heater 25 is removed from the upper casing section II; operation of the vacuum pumping apparatus associated with the evacuation conduit 45 is arrested; and the operation of the cooling arrangement is continued until the molecular still ID has been cooled to the ambient temperature. The operation of the cooling arrangement is then arrested and the molecular still I is disconnected from the associated parts and transferred to a dry cabinet containing 002 or a suitable inert gas. The molecular still I0 is then opened and the UC16 in the lower container 33 is collected and bottled in an atmosphere of CO2 or in a vacuum, and sealed for future use. In so handling the hygroscopic materials, any suitable remotely controlled means, the exact nature of which forms no novel portion of our invention, may be used. The residue remaining in the upper container 32 may be separately collected and subsequently re-worked in order to produce any standard uranium compound such, for example, as UCls, in any suitable manner. The precautions mentioned must be taken in view of the fact that the UCls is extremely hygroscopic and decomposes in the presence of ordinary air containing moisture.

In employing the molecular still ID in the manner described above, wherein the upper container 32 is adapted to accommodate a charge of 1500 grams of UCls, a time interval of approximately fourteen hours is normally required in order to obtain substantially complete sublimation of the chemically pure UCls in the charge. Charges containing as much as five per cent impurities may be readily purified in order to produce substantially chemically pure UCls, the product analyzing as high as 99.6% UCls.

While the still constituting the present invention has been described herein in conjunction with the treatment of U014, UC15, and UCle by procedures that 'include steps of vaporization and/or sublimation of these compounds, it will of course be readily understood that this is mere- 12 ly by way of illustration, and that the still is of general utility and may be employed wherever it is desired to process other materials having generally similar volatilization characteristics.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second removable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receive a charge to be vaporized, said second container being arranged in heat exchange relation with said second casing section and adapted to receive and condense the vapor, and means arranged in heat exchange relation with said first casing section for defining a vapor passage communicating between said first and second containers.

2. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second removable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receive a charge to be vaporized, said second container being arranged in heat exchange relation with said second casing section and adapted to receive and condense the vapor, means arranged in heat exchange relation with said first casing section for definining a vapor passage communicating between said first and second containers, and an evacuation conduit secured to said second casing section and communicating with said enclosure, said second container having an opening formed therein adapted to register with said evacuation conduit.

3. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second removable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receive a charge to be vaporized, said second container being arranged in heat exchange relation with said casing section and adapted to receive and condense the vapor, means arranged in heat exchange relation with said first casing section for defining a vapor passage communicating between said first and second containers, an evacuation conduit secured to said second casing section and communicating with said enclosure, said second container having an opening formed therein adapted to register with said evacuation conduit, and means including removable bafiie structure positioned within said second container for preventing unrestricted flow of the vapor therein through said opening into said evacuation conduit.

4. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second removable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receve a charge to be vaporized, said second container being arranged. in heat exchange relation with said second casing section and adapted to receive and condense the vapor, and means including a wall of said first casing section for defining a vapor passage communicating between said first and second containers.

5. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second re-- movable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receive a charge to be vaporized, said second container being arranged in heat exchange relation with said second casing section and adapted to receive and condense the vapor, and means including a wall of said first container for defining a vapor passage communicating between said first and second containers.

6. A still comprising an upper inverted substantially cup-shaped casing section, a lower substantially cup-shaped casing section, means for securing together said upper and lower cas ing sections to form an hermetically sealed enclosure, means for heating said upper casing section, means for cooling said lower casing section, removable upper and lower substantially cupshaped containers positioned within said enclosure, said upper container being arranged in heat exchange relation with said upper casing section and adapted to receive a charge to be vaporized, said lower container being arranged in heat exchange relation with said lower casin section and adapted to receive and condense the vapor, and means including a wall of said upper casing section and a wall of said upper container arranged in spaced apart relation for defining a vapor passage communicating between said upper and lower containers.

7. A still comprising an upper inverted substantially cup-shaped casing section, a lower substantially cup-shaped casing section, means for securing together said upper and lower casing sections to form an hermetically sealed enclosure, means for heating said upper casing section, means for cooling said lower casing section, a removable lower substantially cup-shaped container positioned within said enclosure and supported by said lower casing section, a removable upper substantially cup-shaped container positioned within said enclosure and supported by said lower container, the side wall of said upper container being arranged in heat exchange relation with said upper casing section and adapted to receive a charge to be vaporized, the side wall of said lower container being arranged in heat exchange relation with said lower casing section and adapted to receive and condense the vapor, and means including a depression formed in the side wall of said upper container and the adjacent side wall of said upper casing section for defining a vapor passage communicating between sid upper and lower containers.

8. A still comprising an upper inverted substantially cup-shaped casing section, a lower substantially cup-shaped casing section, means for securing together said upper and lower casing sections to form an hermetically sealed enclosure, means for heating said upper casing section, means for cooling said lower casing section, removable upper and lower substantially cupshaped containers positioned within said enclosure, the side wall of said upper container being arranged in heat exchange relation with the side wall of said upper casing section, partition structure arranged within the side wall of said upper container and defining a number of compartments adapted to receive a charge to be vaporized, said partition structure being arranged in heat exchange relation with the side wall of said upper container in order to insure substantially uniform heating of the charge in said compartments, the side wall of said lower container being arranged in heat exchange relation with the side wall of said lower casing section, said lower container being adapted to receive and condense the vapor, and means arranged in heat exchange relation with the side wall of said upper casing section for defining a vapor passage communicating between said upper and lower containers.

9. A still comprising first and second casing sections adapted to be secured together to form an hermetically sealed enclosure, means for heating said first casing section, means for cooling said second casing section, first and second removable containers positioned within said enclosure, said first container being arranged in heat exchange relation with said first casing section and adapted to receive a charge to be vaporized, said second container being arranged in heat exchange relation with said second casing section and adapted to receive and condense the vapor, means defining a vapor passage communicating between said first and second containers, and means including a recess formed in the wall of said first casing section for minimizing the flow of heat therefrom into said second casing section.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 491,028 Grow Jan. 31, 1893 497,742 Allderdice May 16, 1893 744,367 Lantreppe Nov. 17, 1903 787,093 Gathmann Apr. 11, 1905 1,013,936 Harsh Jan. 9, 1912 1,312,743 Moeys Aug. 12, 1919 1,359,276 Rushworth NOV. 16, 1920 1,544,383 Epperecht June 30, 1925 2,109,129 Fawcett et al. Feb. 22, 1938 2,178,685 Gage Nov. 7, 1939 2,180,050 Hickman Nov. 14, 1939 2,224,061 Pechukas Dec. 3, 1940 2,258,374 Amati Oct. 7, 1941 2,282,654 Horner May 12, 1942 2,289,956 Gans et al. July 12, 1942 2,304,463 Maier Dec. 8, 1942 2,313,546 Hickman Mar. 9, 1943 2,357,869 Beckwith Sept. 12, 1944 

1. A STILL COMPRISING FIRST AND SECOND CASING SECTIONS, ADAPTED TO BE SECURED TOGETHER TO FROM AN HERMETICALLY SEALED ENCLOSURE, MEANS FOR HEATING SAID FIRST CASING SECTION, MEANS FOR COOLING SAID SECOND CASING SECTION, FIRST AND SECOND REMOVABLE CONTAINERS POSITIONED WITHIN SAID ENCLOSURE, SAID FIRST CONTAINER BEING ARRANGED IN HEAT EXCHANGE RELATION WITH SAID FIRST CASING SECTION AND ADAPTED TO RECEIVE A CHANGE TO BE VAPORIZED, SAID SECOND CONTAINER BEING ARRANGED IN 